Agatoxins: ion channel specific toxins from the american funnel web spider, Agelenopsis aperta

Multiple pathways for high voltage-activated ca(2+) influx in anterior pituitary lactotrophs and somatotrophs

The present study demonstrates that a significant proportion of high voltage-activated (HVA) Ca(2+) influx in native rat anterior pituitary cells is carried through non-L-type Ca(2+) channels. Using whole-cell patch-clamp recordings and specific Ca(2+) channel toxin blockers, we show that approximately 35% of the HVA Ca(2+) influx in somatotrophs and lactotrophs is carried through Ca(v) 2.1, Ca(v) 2.2 and Ca(v) 2.3 channels, and that somatotrophs and lactotrophs share similar proportions of these non-L-type Ca(2+) channels. Furthermore, experiments on mixed populations of native anterior pituitary cells revealed that the fraction of HVA Ca(2+) influx carried through these non-L-type Ca(2+) channels might even be higher (approximately 46%), suggesting that non-L-type channels exist in the majority of native anterior pituitary cells. Using western blotting, immunoblots for α(1C) , α(1D) , α(1A) , α(1B) and α(1E) Ca(2+) channel subunits were identified in native rat anterior pituitary cells. Additionally, using reverse transcriptase-polymerase chain reaction, cDNA transcripts for α(1C) , α(1D) , α(1A) and α(1B) Ca(2+) channel subunits were identified. Transcripts for α(1E) were nonspecific and transcripts for α(1S) were not detected at all (control). Taken together, these results clearly demonstrate the existence of multiple HVA Ca(2+) channels in the membrane of rat native anterior pituitary cells. Whether these channels are segregated among different membrane compartments was investigated further in flotation assays, demonstrating that Ca(v) 2.1, Ca(v) 1.2 and caveolin-1 were mostly localised in light fractions of Nycodenz gradients (i.e. in lipid raft domains). Ca(v) 1.3 channels were distributed among both light and heavy fractions of the gradients (i.e. among raft and nonraft domains), whereas Ca(v) 2.2 and Ca(v) 2.3 channels were distributed mostly among nonraft domains. In summary, in the present study, we demonstrate multiple pathways for HVA Ca(2+) influx through L-type and non-L-type Ca(2+) channels in the membrane of native anterior pituitary cells. The compartmentalisation of these channels among raft and nonraft membrane domains might be essential for their proper regulation by separate receptors and signalling pathways.

High yield production and refolding of the double-knot toxin, an activator of TRPV1 channels

A unique peptide toxin, named double-knot toxin (DkTx), was recently purified from the venom of the tarantula Ornithoctonus huwena and was found to stably activate TRPV1 channels by targeting the outer pore domain. DkTx has been shown to consist of two inhibitory cysteine-knot (ICK) motifs, referred to as K1 and K2, each containing six cysteine residues. Beyond this initial characterization, however, the structural and functional details about DkTx remains elusive in large part due to the lack of a high yielding methodology for the synthesis and folding of this cysteine-rich peptide. Here, we overcome this obstacle by generating pure DkTx in quantities sufficient for structural and functional analyses. Our methodology entails expression of DkTx in E. coli followed by oxidative folding of the isolated linear peptide. Upon screening of various oxidative conditions for optimizing the folding yield of the toxin, we observed that detergents were required for efficient folding of the linear peptide. Our synthetic DkTx co-eluted with the native toxin on HPLC, and irreversibly activated TRPV1 in a manner identical to native DkTx. Interestingly, we find that DkTx has two interconvertible conformations present in a 1∶6 ratio at equilibrium. Kinetic analysis of DkTx folding suggests that the K1 and K2 domains influence each other during the folding process. Moreover, the CD spectra of the toxins shows that the secondary structures of K1 and K2 remains intact even after separating the two knots. These findings provide a starting point for detailed studies on the structural and functional characterization of DkTx and utilization of this toxin as a tool to explore the elusive mechanisms underlying the polymodal gating of TRPV1.

Elucidating nature's solutions to heart, lung, and blood diseases and sleep disorders

Evolution has provided a number of animal species with extraordinary phenotypes. Several of these phenotypes allow species to survive and thrive in environmental conditions that mimic disease states in humans. The study of evolved mechanisms responsible for these phenotypes may provide insights into the basis of human disease and guide the design of new therapeutic approaches. Examples include species that tolerate acute or chronic hypoxemia like deep-diving mammals and high-altitude inhabitants, as well as those that hibernate and interrupt their development when exposed to adverse environments. The evolved traits exhibited by these animal species involve modifications of common biological pathways that affect metabolic regulation, organ function, antioxidant defenses, and oxygen transport. In 2006, the National Heart, Lung, and Blood Institute released a funding opportunity announcement to support studies that were designed to elucidate the natural molecular and cellular mechanisms of adaptation in species that tolerate extreme environmental conditions. The rationale for this funding opportunity is detailed in this article, and the specific evolved mechanisms examined in the supported research are described. Also highlighted are past medical advances achieved through the study of animal species that have evolved extraordinary phenotypes as well as the expectations for new understanding of nature's solutions to heart, lung, blood, and sleep disorders through future research in this area.

Spider-venom peptides as bioinsecticides

Over 10,000 arthropod species are currently considered to be pest organisms. They are estimated to contribute to the destruction of ~14% of the world's annual crop production and transmit many pathogens. Presently, arthropod pests of agricultural and health significance are controlled predominantly through the use of chemical insecticides. Unfortunately, the widespread use of these agrochemicals has resulted in genetic selection pressure that has led to the development of insecticide-resistant arthropods, as well as concerns over human health and the environment. Bioinsecticides represent a new generation of insecticides that utilise organisms or their derivatives (e.g., transgenic plants, recombinant baculoviruses, toxin-fusion proteins and peptidomimetics) and show promise as environmentally-friendly alternatives to conventional agrochemicals. Spider-venom peptides are now being investigated as potential sources of bioinsecticides. With an estimated 100,000 species, spiders are one of the most successful arthropod predators. Their venom has proven to be a rich source of hyperstable insecticidal mini-proteins that cause insect paralysis or lethality through the modulation of ion channels, receptors and enzymes. Many newly characterized insecticidal spider toxins target novel sites in insects. Here we review the structure and pharmacology of these toxins and discuss the potential of this vast peptide library for the discovery of novel bioinsecticides.

Molecular Cloning and Sequence Analysis of the cDNAs Encoding Toxin-Like Peptides from the Venom Glands of Tarantula Grammostola rosea

Tarantula venom glands produce a large variety of bioactive peptides. Here we present the identification of venom components obtained by sequencing clones isolated from a cDNA library prepared from the venom glands of the Chilean common tarantula, Grammostola rosea. The cDNA sequences of about 1500 clones out of 4000 clones were analyzed after selection using several criteria. Forty-eight novel toxin-like peptides (GTx1 to GTx7, and GTx-TCTP and GTx-CRISP) were predicted from the nucleotide sequences. Among these peptides, twenty-four toxins are ICK motif peptides, eleven peptides are MIT1-like peptides, and seven are ESTX-like peptides. Peptides similar to JZTX-64, aptotoxin, CRISP, or TCTP are also obtained. GTx3 series possess a cysteine framework that is conserved among vertebrate MIT1, Bv8, prokineticins, and invertebrate astakines. GTx-CRISP is the first CRISP-like protein identified from the arthropod venom. Real-time PCR revealed that the transcripts for TCTP-like peptide are expressed in both the pereopodal muscle and the venom gland. Furthermore, a unique peptide GTx7-1, whose signal and prepro sequences are essentially identical to those of HaTx1, was obtained.

Neurotoxins and their binding areas on voltage-gated sodium channels

Voltage-gated sodium channels (VGSCs) are large transmembrane proteins that conduct sodium ions across the membrane and by doing so they generate signals of communication between many kinds of tissues. They are responsible for the generation and propagation of action potentials in excitable cells, in close collaboration with other channels like potassium channels. Therefore, genetic defects in sodium channel genes can cause a wide variety of diseases, generally called “channelopathies.” The first insights into the mechanism of action potentials and the involvement of sodium channels originated from Hodgkin and Huxley for which they were awarded the Nobel Prize in 1963. These concepts still form the basis for understanding the function of VGSCs. When VGSCs sense a sufficient change in membrane potential, they are activated and consequently generate a massive influx of sodium ions. Immediately after, channels will start to inactivate and currents decrease. In the inactivated state, channels stay refractory for new stimuli and they must return to the closed state before being susceptible to a new depolarization. On the other hand, studies with neurotoxins like tetrodotoxin (TTX) and saxitoxin (STX) also contributed largely to our today’s understanding of the structure and function of ion channels and of VGSCs specifically. Moreover, neurotoxins acting on ion channels turned out to be valuable lead compounds in the development of new drugs for the enormous range of diseases in which ion channels are involved. A recent example of a synthetic neurotoxin that made it to the market is ziconotide (Prialt^®, Elan). The original peptide, ω-MVIIA, is derived from the cone snail Conus magus and now FDA/EMA-approved for the management of severe chronic pain by blocking the N-type voltage-gated calcium channels in pain fibers. This review focuses on the current status of research on neurotoxins acting on VGSC, their contribution to further unravel the structure and function of VGSC and their potential as novel lead compounds in drug development.

Small molecules from spiders used as chemical probes

Spiders are important species in ecological systems and as major predators of insects they are endowed with a plethora of low-molecular-weight natural products having intriguing biological activities. The isolation and biological characterization of these entities are well established, however, only very recently have these compounds been used as templates for the design, synthesis, and biological evaluation of synthetic analogues. In contrast, the investigation of compounds responsible for chemical communication between spiders is far less developed, but recently new light has been shed onto the area of pheromones and allomones from spiders. Herein, we recapitulate these recent results, put them into perspective with previous findings, and provide an outlook for future studies of these chemotypes.

Characterization of voltage-dependent calcium channel blocking peptides from the venom of the tarantula Grammostola rosea

Voltage-dependent calcium channel blocking peptides were purified and sequenced from the venom of the tarantula, Grammostola rosea. cDNAs encoding the peptide sequences were cloned from the venom gland cDNA library. The electrophysiological effects of the peptides on several types of voltage-dependent calcium channels were evaluated using a Xenopus laevis oocyte expression system. A peptide contained in one of the HPLC peak fractions inhibited P/Q type voltage-dependent calcium channels (Ca(v)2.1). The amino acid sequence of this peptide is identical to that of ω-grammotoxin SIA. A peptide from another discrete peak, which is identical to GsAFII except for one tryptophan residue in the C-terminus, inhibited L-type voltage-dependent calcium channels (Ca(v)1.2). A novel peptide, named GTx1-15 (Accession number, AB201016), shows 76.5% sequence homology with the sodium channel blocker phrixotoxin 3, however, GTx1-15 preferentially inhibited T-type voltage-dependent calcium channels (Ca(v)3.1). In silico secondary and tertiary structure prediction revealed that GTx1-15 and sodium channel blockers such as hainantoxin-IV, phrixotoxin 3, and ceratotoxin 2 show very similar β-strand composition, distribution of Optimal Docking Areas (continuous surface patches likely to be involved in protein-protein interactions), and surface electrostatic potential. These findings suggest that these peptide toxins evolved from common ancestors by gene duplication to maintain surface atmospheres appropriate for interaction with low-voltage-dependent ion channels.

Peptide neurotoxins that affect voltage-gated calcium channels: a close-up on ω-agatoxins

Peptide neurotoxins found in animal venoms have gained great interest in the field of neurotransmission. As they are high affinity ligands for calcium, potassium and sodium channels, they have become useful tools for studying channel structure and activity. Peptide neurotoxins represent the clinical potential of ion-channel modulators across several therapeutic fields, especially in developing new strategies for treatment of ion channel-related diseases. The aim of this review is to overview the latest updates in the domain of peptide neurotoxins that affect voltage-gated calcium channels, with a special focus on ω-agatoxins.

Spider-venom peptides as therapeutics

Spiders are the most successful venomous animals and the most abundant terrestrial predators. Their remarkable success is due in large part to their ingenious exploitation of silk and the evolution of pharmacologically complex venoms that ensure rapid subjugation of prey. Most spider venoms are dominated by disulfide-rich peptides that typically have high affinity and specificity for particular subtypes of ion channels and receptors. Spider venoms are conservatively predicted to contain more than 10 million bioactive peptides, making them a valuable resource for drug discovery. Here we review the structure and pharmacology of spider-venom peptides that are being used as leads for the development of therapeutics against a wide range of pathophysiological conditions including cardiovascular disorders, chronic pain, inflammation, and erectile dysfunction.

Molecular diversity of spider venom

Spider venom, a factor that has played a decisive role in the evolution of one of the most successful groups of living organisms, is reviewed. Unique molecular diversity of venom components including substances of variable structure (from simple low molecular weight compounds to large multidomain proteins) with different functions is considered. Special attention is given to the structure, properties, and biosynthesis of toxins of polypeptide nature.

Unique bell-shaped voltage-dependent modulation of Na+ channel gating by novel insect-selective toxins from the spider Agelena orientalis

Spider venoms provide a highly valuable source of peptide toxins that act on a wide diversity of membrane-bound receptors and ion channels. In this work, we report isolation, biochemical analysis, and pharmacological characterization of a novel family of spider peptide toxins, designated beta/delta-agatoxins. These toxins consist of 36-38 amino acid residues and originate from the venom of the agelenid funnel-web spider Agelena orientalis. The presented toxins show considerable amino acid sequence similarity to other known toxins such as mu-agatoxins, curtatoxins, and delta-palutoxins-IT from the related spiders Agelenopsis aperta, Hololena curta, and Paracoelotes luctuosus. beta/delta-Agatoxins modulate the insect Na(V) channel (DmNa(V)1/tipE) in a unique manner, with both the activation and inactivation processes being affected. The voltage dependence of activation is shifted toward more hyperpolarized potentials (analogous to site 4 toxins) and a non-inactivating persistent Na(+) current is induced (site 3-like action). Interestingly, both effects take place in a voltage-dependent manner, producing a bell-shaped curve between -80 and 0 mV, and they are absent in mammalian Na(V) channels. To the best of our knowledge, this is the first detailed report of peptide toxins with such a peculiar pharmacological behavior, clearly indicating that traditional classification of toxins according to their binding sites may not be as exclusive as previously assumed.

ArachnoServer: a database of protein toxins from spiders

BACKGROUND

Venomous animals incapacitate their prey using complex venoms that can contain hundreds of unique protein toxins. The realisation that many of these toxins may have pharmaceutical and insecticidal potential due to their remarkable potency and selectivity against target receptors has led to an explosion in the number of new toxins being discovered and characterised. From an evolutionary perspective, spiders are the most successful venomous animals and they maintain by far the largest pool of toxic peptides. However, at present, there are no databases dedicated to spider toxins and hence it is difficult to realise their full potential as drugs, insecticides, and pharmacological probes.

DESCRIPTION

We have developed ArachnoServer, a manually curated database that provides detailed information about proteinaceous toxins from spiders. Key features of ArachnoServer include a new molecular target ontology designed especially for venom toxins, the most up-to-date taxonomic information available, and a powerful advanced search interface. Toxin information can be browsed through dynamic trees, and each toxin has a dedicated page summarising all available information about its sequence, structure, and biological activity. ArachnoServer currently manages 567 protein sequences, 334 nucleic acid sequences, and 51 protein structures.

CONCLUSION

ArachnoServer provides a single source of high-quality information about proteinaceous spider toxins that will be an invaluable resource for pharmacologists, neuroscientists, toxinologists, medicinal chemists, ion channel scientists, clinicians, and structural biologists. ArachnoServer is available online at http://www.arachnoserver.org.

Expression and characterization of jingzhaotoxin-34, a novel neurotoxin from the venom of the tarantula Chilobrachys jingzhao

Jingzhaotoxin-34 (JZTX-34) is a 35-residue polypeptide from the venom of Chinese tarantula Chilobrachys jingzhao. Our previous work reported its full-length cDNA sequence encoding a precursor with 87 residues. In this study we report the protein expression and biological function characterization. The toxin was efficiently expressed by the secretary pathway in yeast. Under whole-cell patch-clamp mode, the expressed JZTX-34 was able to inhibit tetrodotoxin-sensitive (TTX-S) sodium currents (IC(50) approximately 85 nM) while having no significant effects on tetrodotoxin-resistant (TTX-R) sodium currents on rat dorsal root ganglion neurons. The inhibition of TTX-S sodium channels was completely reversed by strong depolarization (+120 mV). Toxin treatment altered neither channel activation and inactivation kinetics nor recovery rate from inactivation. However, it is interesting to note that in contrast to huwentoxin-IV, a recently identified receptor site-4 toxin from Ornithoctonus huwena venom, 100 nM JZTX-34 caused a negative shift of steady-state inactivation curve of TTX-S sodium channels by approximately 10 mV. The results indicated that JZTX-34 might inhibit mammalian sensory neuronal sodium channels through a mechanism similar to HWTX-IV by trapping the IIS4 voltage sensor in the resting conformation, but their binding sites should not overlay completely.

Molecular evolution, functional variation, and proposed nomenclature of the gene family that includes sphingomyelinase D in sicariid spider venoms

The venom enzyme sphingomyelinase D (SMase D) in the spider family Sicariidae (brown or fiddleback spiders [Loxosceles] and six-eyed sand spiders [Sicarius]) causes dermonecrosis in mammals. SMase D is in a gene family with multiple venom-expressed members that vary in functional specificity. We analyze molecular evolution of this family and variation in SMase D activity among crude venoms using a data set that represents the phylogenetic breadth of Loxosceles and Sicarius. We isolated a total of 190 nonredundant nucleotide sequences encoding 168 nonredundant amino acid sequences of SMase D homologs from 21 species. Bayesian phylogenies support two major clades that we name alpha and beta, within which we define seven and three subclades, respectively. Sequences in the alpha clade are exclusively from New World Loxosceles and Loxosceles rufescens and include published genes for which expression products have SMase D and dermonecrotic activity. The beta clade includes paralogs from New World Loxosceles that have no, or reduced, SMase D and no dermonecrotic activity and also paralogs from Sicarius and African Loxosceles of unknown activity. Gene duplications are frequent, consistent with a birth-and-death model, and there is evidence of purifying selection with episodic positive directional selection. Despite having venom-expressed SMase D homologs, venoms from New World Sicarius have reduced, or no, detectable SMase D activity, and Loxosceles in the Southern African spinulosa group have low SMase D activity. Sequence conservation mapping shows >98% conservation of proposed catalytic residues of the active site and around a plug motif at the opposite end of the TIM barrel, but alpha and beta clades differ in conservation of key residues surrounding the apparent substrate binding pocket. Based on these combined results, we propose an inclusive nomenclature for the gene family, renaming it SicTox, and discuss emerging patterns of functional diversification.

Synthesis of cyclooctapeptides: constraints analogues of the peptidic neurotoxin, omega-agatoxine IVB-an experimental point of view

omega-AGA IVB is an important lead structure when considering the design of effectors of glutamate release inducting P/Q-type calcium channels. The best route to achieve the analogues possessing the three-dimensional arrangement corresponding to the native binding loop was the introduction of constraint by ring formation via side chain to side chain lactamization for suitably protected Lys and Glu residues. Since tryptophane residue located at position 14 of this neuropeptide has been suggested as essential for binding, analogues in which this amino acid was replaced by aza-tryptophane and alanine were synthesized. The synthesis was carried out on various acid-labile resins (BARLOS chlorotrityl, Rink amide, PEG-based or Wang resins), by Fmoc strategy. In this paper, we describe optimization of the peptide cyclization with various protecting groups, and on resin or in solution cyclization experimental parameters.

ω-Lsp-IA, a novel modulator of P-type Ca2+ channels

A novel polypeptide, designated omega-Lsp-IA, which modulates P-type Ca(2+) channels, was purified from the venom of the spider Geolycosa sp. omega-Lsp-IA contains 47 amino acid residues and 4 intramolecular disulfide bridges. It belongs to a group of spider toxins affecting Ca(2+) channels and presumably forms the inhibitor cystine knot (ICK) fold. Peculiar structural features (a cluster of positively charged residues in the C-terminal loop of the peptide and a regular distribution of hydrophobic residues) that may play a decisive role in the omega-Lsp-IA mechanism of action were located. Recombinant omega-Lsp-IA was produced in prokaryotic expression system and was shown to be structurally and functionally identical to the native toxin. At saturating concentration (10nM), the peptide clearly slows down the activation kinetics and partially inhibits the amplitude of P-current in rat cerebellar Purkinje neurons. Prominent deceleration of the activation kinetics is manifested as the appearance of a five-fold slower component of the current activation. The specificity of action of omega-Lsp-IA on different Ca(2+) channel types was studied in isolated hippocampal neurons of rat. omega-Agatoxin IVA completely removed the effect of omega-Lsp-IA on the whole-cell Ca(2+) current. Therefore, omega-Lsp-IA appears to act specifically on P-type Ca(2+) channels.

Painful toxins acting at TRPV1

Many plant and animal toxins cause aversive behaviors in animals due to their pungent or unpleasant taste or because they cause other unpleasant senstations like pain. This article reviews the current state of knowledge of toxins that act at the TRPV1 ion channel, which is expressed in primary sensory neurons, is activated by multiple painful stimuli and is thought to be a key pain sensor and integrator. The recent finding that painful peptide "vanillotoxin" components of tarantula toxin activate the TRPV1 ion channel to cause pain led us to survey what is known about toxins that act at this receptor. Toxins from plants, spiders and jellyfish are considered. Where possible, structural information about sites of interaction is considered in relation to toxin-binding sites on the Kv ion channel, for which more structural information exists. We discuss a developing model where toxin agonists such as resiniferatoxin and vanillotoxins are proposed to interact with a region of TRPV1 that is homologous to the "voltage sensor" in the Kv1.2 ion channel, to open the channel and activate primary sensory nerves, causing pain.

Peptides of arachnid venoms with insecticidal activity targeting sodium channels

Arachnids have a venom apparatus and secrete a complex chemical mixture of low molecular mass organic molecules, enzymes and polypeptide neurotoxins designed to paralyze or kill their prey. Most of these toxins are specific for membrane voltage-gated sodium channels, although some may also target calcium or potassium channels and other membrane receptors. Scorpions and spiders have provided the greatest number of the neurotoxins studied so far, for which, a good number of primary and 3D structures have been obtained. Structural features, comprising a folding that determines a similar spatial distribution of charged and hydrophobic side chains of specific amino acids, are strikingly common among the toxins from spider and scorpion venoms. Such similarities are, in turn, the key feature to target and bind these proteins to ionic channels. The search for new insecticidal compounds, as well as the study of their modes of action, constitutes a current approach to rationally design novel insecticides. This goal tends to be more relevant if the resistance to the conventional chemical products is considered. A promising alternative seems to be the biotechnological approach using toxin-expressing recombinant baculovirus. Spider and scorpion toxins having insecticidal activity are reviewed here considering their structures, toxicities and action mechanisms in sodium channels of excitable membranes.

CSTX-1, a toxin from the venom of the hunting spider Cupiennius salei, is a selective blocker of L-type calcium channels in mammalian neurons

The inhibitor cystine-knot motif identified in the structure of CSTX-1 from Cupiennius salei venom suggests that this toxin may act as a blocker of ion channels. Whole-cell patch-clamp experiments performed on cockroach neurons revealed that CSTX-1 produced a slow voltage-independent block of both mid/low- (M-LVA) and high-voltage-activated (HVA) insect Ca(v) channels. Since C. salei venom affects both insect as well as rodent species, we investigated whether Ca(v) channel currents of rat neurons are also inhibited by CSTX-1. CSTX-1 blocked rat neuronal L-type, but no other types of HVA Ca(v) channels, and failed to modulate LVA Ca(v) channel currents. Using neuroendocrine GH3 and GH4 cells, CSTX-1 produced a rapid voltage-independent block of L-type Ca(v) channel currents. The concentration-response curve was biphasic in GH4 neurons and the subnanomolar IC(50) values were at least 1000-fold lower than in GH3 cells. L-type Ca(v) channel currents of skeletal muscle myoballs and other voltage-gated ion currents of rat neurons, such as I(Na(v)) or I(K(v)) were not affected by CSTX-1. The high potency and selectivity of CSTX-1 for a subset of L-type channels in mammalian neurons may enable the toxin to be used as a molecular tool for the investigation of this family of Ca(v) channels.

Modulation of insect Cav channels by peptidic spider toxins

Insects have a much smaller repertoire of voltage-gated calcium (Ca(V)) channels than vertebrates. Drosophila melanogaster harbors only a single ortholog of each of the vertebrate Ca(V)1, Ca(V)2, and Ca(V)3 subtypes, although its basal inventory is expanded by alternative splicing and editing of Ca(V) channel transcripts. Nevertheless, there appears to be little functional plasticity within this limited panel of insect Ca(V) channels, since severe loss-of-function mutations in genes encoding the pore-forming alpha1 subunits in Drosophila are embryonic lethal. Since the primary role of spider venom is to paralyze or kill insect prey, it is not surprising that most, if not all, spider venoms contain peptides that potently modify the activity of these functionally critical insect Ca(V) channels. Unfortunately, it has proven difficult to determine the precise ion channel subtypes recognized by these peptide toxins since insect Ca(V) channels have significantly different pharmacology to their vertebrate counterparts, and cloned insect Ca(V) channels are not available for electrophysiological studies. However, biochemical and genetic studies indicate that some of these spider toxins might ultimately become the defining pharmacology for certain subtypes of insect Ca(V) channels. This review focuses on peptidic spider toxins that specifically target insect Ca(V) channels. In addition to providing novel molecular tools for ion channel characterization, some of these toxins are being used as leads to develop new methods for controlling insect pests.

Insect-selective spider toxins targeting voltage-gated sodium channels

The voltage-gated sodium (Na(v)) channel is a target for a number of drugs, insecticides and neurotoxins. These bind to at least seven identified neurotoxin binding sites and either block conductance or modulate Na(v) channel gating. A number of peptide neurotoxins from the venoms of araneomorph and mygalomorph spiders have been isolated and characterized and determined to interact with several of these sites. These all conform to an 'inhibitor cystine-knot' motif with structural, but not sequence homology, to a variety of other spider and marine snail toxins. Of these, spider toxins several show phyla-specificity and are being considered as lead compounds for the development of biopesticides. Hainantoxin-I appears to target site-1 to block Na(v) channel conductance. Magi 2 and Tx4(6-1) slow Na(v) channel inactivation via an interaction with site-3. The delta-palutoxins, and most likely mu-agatoxins and curtatoxins, target site-4. However, their action is complex with the mu-agatoxins causing a hyperpolarizing shift in the voltage-dependence of activation, an action analogous to scorpion beta-toxins, but with both delta-palutoxins and mu-agatoxins slowing Na(v) channel inactivation, a site-3-like action. In addition, several other spider neurotoxins, such as delta-atracotoxins, are known to target both insect and vertebrate Na(v) channels most likely as a result of the conserved structures within domains of voltage-gated ion channels across phyla. These toxins may provide tools to establish the molecular determinants of invertebrate selectivity. These studies are being greatly assisted by the determination of the pharmacophore of these toxins, but without precise identification of their binding site and mode of action their potential in the above areas remains underdeveloped.

?-Conotoxin CVIB differentially inhibits native and recombinant N- and P/Q-type calcium channels

Omega-conotoxins are routinely used as selective inhibitors of different classes of voltage-gated calcium channels (VGCCs) in excitable cells. In the present study, we examined the potent N-type VGCC antagonist omega-conotoxin CVID and non-selective N- and P/Q-type antagonist CVIB for their ability to block native VGCCs in rat dorsal root ganglion (DRG) neurons and recombinant VGCCs expressed in Xenopus oocytes. Omega-conotoxins CVID and CVIB inhibited depolarization-activated whole-cell VGCC currents in DRG neurons with pIC50 values of 8.12 +/- 0.05 and 7.64 +/- 0.08, respectively. Inhibition of Ba2+ currents in DRG neurons by CVID (approximately 66% of total) appeared to be irreversible for > 30 min washout, whereas Ba2+ currents exhibited rapid recovery from block by CVIB (> or = 80% within 3 min). The recoverable component of the Ba2+ current inhibited by CVIB was mediated by the N-type VGCC, whereas the irreversibly blocked current (approximately 22% of total) was attributable to P/Q-type VGCCs. Omega-conotoxin CVIB reversibly inhibited Ba2+ currents mediated by N- (Ca(V)2.2) and P/Q- (Ca(V)2.1), but not R- (Ca(V)2.3) type VGCCs expressed in Xenopus oocytes. The alpha2delta1 auxiliary subunit co-expressed with Ca(V)2.2 and Ca(V)2.1 reduced the sensitivity of VGCCs to CVIB but had no effect on reversibility of block. Determination of the NMR structure of CVIB identified structural differences to CVID that may underlie differences in selectivity of these closely related conotoxins. Omega-conotoxins CVIB and CVID may be useful as antagonists of N- and P/Q-type VGCCs, particularly in sensory neurons involved in processing primary nociceptive information.

Age and diet influence the composition of venom from the endoparasitic wasp Pimpla turionellae L. (Hymenoptera: Ichneumonidae)

Venom from the endoparasitic wasp Pimpla turionellae L. (Hymenoptera: Ichneumonidae) was found to contain a complex mixture of biogenic amines, noradrenalin, phospholipase B, and several proteins and peptides. The amount of noradrenalin and serotonin was found to be highest in venom from newly emerged wasps and decreased with age. Histamine was detected in minute amounts in comparison to the other venom components, and declined with increasing age of the parasitoids. Total peptides and proteins detected by reversed-phase HPLC increased with host age. Old-aged (30-33 days after emergence) wasps contained 2-fold more phospholipase B than young (<10 days [d] old) or medium-aged (10-22-d-old) females. Increases in phospholipase B alone, however, did not account for all changes in total venom protein because by 40 days after emergence, the levels of this enzyme began to decline while the amount of total protein was higher than in younger wasps. For all venom components detected, the amount present in the venom sharply decreased following host exposure. This was presumed to be the result of venom depletion associated with envenomation. Consistent with this view were the modest increases in venom components in wasps displaying a decreased rate of parasitization. When adult females were offered honey alone or in combination with feeding on hosts, no significant changes in venom composition were observed, with the exception of noradrenalin, which was found to be 5 times higher in concentration in wasps fed honey only. These results suggest that wasp age and incidence of parasitism are more important features influencing the composition of venom than the diet of adult females.

A Command Chemical Triggers an Innate Behavior by Sequential Activation of Multiple Peptidergic Ensembles

BACKGROUND

At the end of each molt, insects shed their old cuticle by performing the ecdysis sequence, an innate behavior consisting of three steps: pre-ecdysis, ecdysis, and postecdysis. Blood-borne ecdysis-triggering hormone (ETH) activates the behavioral sequence through direct actions on the central nervous system.

RESULTS

To elucidate neural substrates underlying the ecdysis sequence, we identified neurons expressing ETH receptors (ETHRs) in Drosophila. Distinct ensembles of ETHR neurons express numerous neuropeptides including kinin, FMRFamides, eclosion hormone (EH), crustacean cardioactive peptide (CCAP), myoinhibitory peptides (MIP), and bursicon. Real-time imaging of intracellular calcium dynamics revealed sequential activation of these ensembles after ETH action. Specifically, FMRFamide neurons are activated during pre-ecdysis; EH, CCAP, and CCAP/MIP neurons are active prior to and during ecdysis; and activity of CCAP/MIP/bursicon neurons coincides with postecdysis. Targeted ablation of specific ETHR ensembles produces behavioral deficits consistent with their proposed roles in the behavioral sequence.

CONCLUSIONS

Our findings offer novel insights into how a command chemical orchestrates an innate behavior by stepwise recruitment of central peptidergic ensembles.

Peptide profiling by matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry of the Lasiodora parahybana tarantula venom gland

In order to establish a venom fingerprint and a peptide profile of the Lasiodora parahybana tarantula venom gland, we used conventional methods such as reversed phase liquid chromatography coupled to an electrospray-ionisation hybrid quadrupole time of flight mass spectrometer (LC/ESI-QqTOFMS), matrix-assisted laser desorption/ionization time-of-flight-MS (MALDI-TOFMS) and direct study of L. parahybana venom by nanospray-ionization QqTOFMS (nanoESI-QqTOFMS) and a new technology for the direct analysis of fresh tissues using MALDI-TOFMS. The analysis of the crude venom allowed the characterization of specific juvenile and adult biomarkers. In situ MALDI analysis of L. parahybana venom gland sections revealed different peptide expression levels all along the gland and non-processed peptide precursors, demonstrating the power of the method for the dynamic investigation of peptide evolution in the venom gland of spiders.

Venom landscapes: mining the complexity of spider venoms via a combined cDNA and mass spectrometric approach

The complexity of Australian funnel-web spider venoms has been explored via the combined use of MALDI-TOF mass spectrometry coupled with chromatographic separation and the analysis of venom-gland cDNA libraries. The results show that these venoms are far more complex than previously realized. We show that the venoms of Australian funnel-web spiders contain many hundreds of peptides that follow a bimodal distribution, with about 75% of the peptides having a mass of 3000-5000 Da. The mass spectral data were validated by matching the experimentally observed masses with those predicted from peptide sequences derived from analysis of venom-gland cDNA libraries. We show that multiple isoforms of these peptides are found in small chromatographic windows, which suggests that the wide distribution of close molecular weights among the chromatographic fractions probably reflects a diversity of structures and physicochemical properties. The combination of all predicted and measured parameters permits the interpretation of three-dimensional 'venom landscapes' derived from LC-MALDI analysis. We propose that these venom landscapes might have predictive value for the discovery of various groups of pharmacologically distinct toxins in complex venoms.

Parasitoid wasp sting: A cocktail of GABA, taurine, and β-alanine opens chloride channels for central synaptic block and transient paralysis of a cockroach host

The wasp Ampulex compressa injects venom directly into the prothoracic ganglion of its cockroach host to induce a transient paralysis of the front legs. To identify the biochemical basis for this paralysis, we separated venom components according to molecular size and tested fractions for inhibition of synaptic transmission at the cockroach cercal-giant synapse. Only fractions in the low molecular weight range (<2 kDa) caused synaptic block. Dabsylation of venom components and analysis by HPLC and MALDI-TOF-MS revealed high levels of GABA (25 mM), and its receptor agonists beta-alanine (18 mM), and taurine (9 mM) in the active fractions. Each component produces transient block of synaptic transmission at the cercal-giant synapse and block of efferent motor output from the prothoracic ganglion, which mimics effects produced by injection of whole venom. Whole venom evokes picrotoxin-sensitive chloride currents in cockroach central neurons, consistent with a GABAergic action. Together these data demonstrate that Ampulex utilizes GABAergic chloride channel activation as a strategy for central synaptic block to induce transient and focal leg paralysis in its host.

Spider venom: enhancement of venom efficacy mediated by different synergistic strategies in Cupiennius salei

Besides the power of the chelicerae, synergistic interactions between different components in the venom of Cupiennius salei ensure the hunting success of this spider. The main components of the venom were tested alone or in combination according to their physiological venom concentrations in Drosophila bioassays. The high K+ ion content of the venom synergistically increases the insecticidal activity of the neurotoxins CSTX-1, CSTX-9 and CSTX-13 by 20% but does not influence the insecticidal effectiveness of the antimicrobially and cytolytically acting cupiennin 1a. Histamine only enhances the activity of the main neurotoxin CSTX-1. An important role in the envenomation process is exhibited by cupiennin 1a, which increases the insecticidal activity of the above-mentioned neurotoxins by up to 65%. Additionally, the highly synergistic effect of the enhancer CSTX-13 on CSTX-1, provoked in non-toxic physiological concentrations, could be verified for CSTX-9, but not for cupiennin 1a. CSTX-1 and CSTX-9 show positive interactions only when both are injected in toxic non-physiological concentrations.

Calcium flux in neuroblastoma cells is a coupling mechanism between non-genomic and genomic modes of estrogens

Estrogens have been demonstrated to rapidly modulate calcium levels in a variety of cell types. However, the significance of estrogen-mediated calcium flux in neuronal cells is largely unknown. The relative importance of intra- and extracellular sources of calcium in estrogenic effects on neurons is also not well understood. Previously, we have demonstrated that membrane-limited estrogens, such as E-BSA given before an administration of a 2-hour pulse of 17beta-estradiol (E2), can potentiate the transcription mediated by E2 from a consensus estrogen response element (ERE)-driven reporter gene. Inhibitors to signal transduction cascades given along with E-BSA or E2 demonstrated that calcium flux is important for E-BSA-mediated potentiation of transcription in a transiently transfected neuroblastoma cell line. In this report, we have used inhibitors to different voltage-gated calcium channels (VGCCs) and to intracellular store receptors along with E-BSA in the first pulse or with E2 in the second pulse to investigate the relative importance of these channels to estrogen-mediated transcription. Neither L- nor P-type VGCCs seem to play a role in estrogen action in these cells; while N-type VGCCs are important in both the non-genomic and genomic modes of estrogen action. Specific inhibitors also showed that the ryanodine receptor and the inositol trisphosphate receptor are important to E-BSA-mediated transcriptional potentiation. This report provides evidence that while intracellular stores of calcium are required to couple non-genomic actions of estrogen initiated at the membrane to transcription in the nucleus, extracellular sources of calcium are also important in both non-genomic and genomic actions of estrogens.